Innovation: Methane capture gives more bang for the buck

Carbon-capture technology has garnered plenty of attention as a means of halting global warming. But while carbon dioxide has become the bête noire of environmentalists, maybe methane shouldn’t be far behind.

But how do you go about getting methane out of the atmosphere? “From a technical point of view it is much more challenging than removing carbon dioxide because of the low concentrations of methane in the atmosphere,” says Alexander Sorokin, a chemist at the University of Lyon in France.

Friendly bacteria

There is hope, however. Methods already exist to remove the high concentrations of methane that are emitted from landfill sites and mines. For example, a type of bacteria called methanotrophs digest methane, producing by-products such as formaldehyde, which can be used in the manufacture of hydrogen fuel.

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“Right now methanotrophs are slow and would need to be speeded up to be useful. Possibly genetic engineering could increase the efficiency,” says Boucher. It may then be possible to use the bacteria to extract methane from the air.

Meanwhile, chemists are looking at ways of mimicking the bacteria. Earlier this year, Amy Rosenzweig, from Northwestern University in Evanston, Illinois, and colleagues, showed that methanotrophs use an enzyme with two copper atoms at its centre to oxidise methane, a finding that could aid the development of methane-removing catalysts.

And in 2008, Sorokin and his colleagues developed an iron-based catalyst that can oxidise high concentrations of methane in water. Removal of methane from water could help to avert disaster if rising sea temperatures melt permafrost or unlock deposits of methane hydrates from their current sea floor location.

Because of its extreme potency as a greenhouse gas, Boucher and Folberth argue that methane removal could be financially competitive with carbon capture, even if the technologies themselves are more expensive.

Added incentives

That’s because, on a like-for-like basis, methane causes around 100 times as much greenhouse warming as carbon dioxide over the first five years that it spends in the atmosphere.

And although methane hangs around for only 10 years compared to 100 years for carbon dioxide, it leaves a nasty legacy&colon; carbon dioxide. That’s because as it degrades, 1 tonne of methane produces 2.75 tonnes of carbon dioxide. On top of this, methane slows down the formation of shade-forming sulphate aerosols.

Since pre-industrial times, methane levels in the atmosphere have risen from around 715 parts per billion to nearly 1800 ppb, claims Folberth. “If methane could be taken back to pre-industrial levels it would bring about half a degree of cooling and would be equivalent to removing one-third of anthropogenic carbon dioxide,” says Folberth. Furthermore, the cooling would take place within 10 years.

Obvious places to begin methane capture might be locations where large volumes of air are already being moved, such as around cooling towers or wind farms, says Kirk Smith, an environmental scientist at the University of California, Berkeley.